The present invention relates to equipment for testing of integrated circuits. More particularly, the present invention relates to a probe card for wafer testing of semiconductor integrated circuits.
In semiconductor integrated circuit manufacturing, it is conventional to test the integrated circuits (“IC's”) during manufacturing and prior to shipment to ensure proper operation. Wafer testing is a well-known testing technique commonly used in production testing of wafer-mounted semiconductor IC's (or “dice”), wherein a temporary electrical current is established between automatic test equipment (ATE) and each IC (or “die”) on the wafer to demonstrate proper performance of the IC's. Exemplary components used in wafer testing include an ATE test board (e.g., a multilayer printed circuit board that is connected to the ATE) that transfers the test signals back and forth between the ATE and a probe card.
An exemplary probe card includes a printed circuit board that generally contains several hundred probe needles positioned to establish electrical contact with a series of connection terminals (or die contacts) on the IC wafer. Known probe cards may also include a substrate or so-called space transformer which electrically connects the probes to the printed circuit board. The space transformer may include a multi-layer ceramic substrate, a multi-layer organic substrate, etc. It is known to mount each of the plurality of flexible probes to a mounting surface of the space transformer. Typically, the probes are mounted to electrically conductive, preferably metallic bonding pads formed on the substrate though conventional plating or etching techniques well known to those of ordinary skill in the art of semiconductor fabrication.
One difficulty in the fabrication of probe cards is that the mounting surface of the space transformer substrate is desirably maintained within a tight flatness tolerance, such that undesirable variation in the positions of the probe tips, which connect with the IC connection terminals, is minimized. Tight positional tolerances of all the probe tips within the probe assembly are crucial for establishing and maintaining identical contacting conditions between the individual probe tips and the terminals of the tested chips. Positional tolerances affect both the position of the probe tips relative to the corresponding terminals and the force required to establish a satisfactory electrical connection between the probes and the IC connection terminals. In order to tightly control positional tolerances of the probe tips, it is desirable that the mounting surface of the plurality of probes be as nearly planar as practicable.
A large probe card is desirable in that a larger probe card can accommodate concurrent testing of a larger number of semiconductor dice or testing of a larger single semiconductor die, and thus increase the efficiency of the testing process. However, as the size of the probe card and the substrate increases, it becomes increasingly difficult to efficiently produce substrates having satisfactory flatness characteristics. For example, as the substrate material is lapped to a desired configuration, residual stresses can be created or relieved. Changes in the stress state of the substrate material can in turn cause warpage of the substrate, which tends to result in larger magnitude flatness deviations as the size of the substrate increases. Furthermore, a non-repairable defect in a relatively large substrate work piece results in more waste, and thus less efficiency, than would occur in a production process having the same defect rate and producing relatively small substrate work pieces. Still further, as the size of the probe card and substrate increases, variation in position of the probe tips from a desired nominal position also increases as the substrate is exposed to temperature variations and undergoes expansion and contraction in accordance with the substrate material's coefficient of thermal expansion properties.
Thus, it would be desirable to provide a probe card and substrate combining relatively large size with satisfactory flatness characteristics, good manufacturing characteristics, and capable of maintaining satisfactory positional tolerances over the expected operating temperature range of the probe card.